RFR: 8295323: Unnecessary HashTable usage in StyleSheet

[Alexey Ivanov]

On Sat, 1 Oct 2022 16:53:17 GMT, Andrey Turbanov <aturbanov at openjdk.org> wrote:

> Hashtable was used only from single thread. And only non-null key/values added to it. We can safely replace it with HashSet.

Looks good to me. All tests pass.

-------------

Marked as reviewed by aivanov (Reviewer).

PR: https://git.openjdk.org/jdk/pull/10522